Method of thermally insulating a cryogenic storage tank

ABSTRACT

Thermal insulation comprised of fiberglass boards or batts having relatively small diameter fiberglass fibers either bound or unbound is wound about the lading container pressure vessel of a tank truck, trailer or rail car. As the insulation is wound about a longitudinal section of the vessel, the insulation is squeezed from its free height to a lesser height to increase the density of the insulation and also permit passage of the outer jacket. The squeezing is preferably accomplished by wrapping each layer of insulation with a continuous wire mesh. The tension is maintained with the use of a long rod intertwined in the wire mesh, which rod is withdrawn after a section of the outer jacket is over a section of the vessel thereby permitting the insulation to expand and substantially fill the void between the vessel and outer jacket.

This is a continuation of application Ser. No. 741,194, filed Nov. 12,1976, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to an improved thermal insulation systemfor mobile cryogenic tanks and the method of installing the thermalinsulation in particular between a lading container vessel and itsassociated outer protective jacket.

Presently the insulation that is used in the vacuum space between thevessel and the jacket of a cryogenic tank is a perlite powder. However,there are at least two disadvantages associated with this form ofinsulation. In the first place, this known insulation has a higherthermal conductivity in the (insulation) pressure range of 5000 micronsof mercury to atmospheric pressure than the system of the presentinvention. Accordingly, one object of the present invention is toprovide a thermal insulation for use in cryogenic vessels such as tanktrucks, trailers, and railroad cars having a relatively low thermalconductivity especially over a pressure range of about 5000 microns ofmercury to atmospheric pressure. This low thermal conductivity over apressure range even up to atmospheric pressure is important in reducingthe heat transfer from ambient to the lading container in the event ashipping vacuum is lost either due to accident or malfunction. This isespecially critical in the transportation of hazardous materials orwhere increased heat transfer may cause premature and excessive ventingof the commodity into the atmosphere.

Another disadvantage associated with the use of powder insulation isthat the powder tends to settle thus exposing parts of the top of thetank which are uninsulated. This causes an increase in heat transfer tothe commodity within the inner vessel. Also, there is no simple way ofdetecting the settling of this powder insulation. The only way to remedythe situation regarding the powder insulation is to open the jacket andrefill the insulation. However, this is a costly and time consumingfurther additional procedure.

Accordingly, another object of the present invention is to provide athermal insulation for a cryogenic tank truck wherein the insulation isnon-settling providing uniform insulation about the entire tank.

A further object of the present invention is to provide an improvedinsulation system for use primarily in insulating cryogenic tank trucks,trailers and railroad cars.

Still another object of the present invention is to provide an improvedmethod of insulating a cryogenic tank container.

SUMMARY OF THE INVENTION

To accomplish the foregoing and other objects of this invention there isprovided a thermal insulation system for use with cryogenic storagetanks such as tank trucks, trailers and railroad cars. This systemcomprises, in combination, a container vessel for the cryogenic liquidand an outer jacket about the vessel and defining a space therebetweenwhich is to be at least partially evacuated for insulation purposes. Thesystem of this invention comprises fiberglass insulation means which iswrapped about the vessel to substantially fill the space. Mesh means isalso wrapped about the fiberglass insulation means for holding thefiberglass insulation means in place.

In accordance with the method of the present invention the containervessel is preferably insulated in three sections including the two endsections and a center section. The insulation system of the invention isessentially installed concurrently with the assembling and weldingtogether of the three sections of the container vessel. The method ofinstalling the insulation is essentially the same for each section ofthe container vessel.

The insulation is wrapped about the cylindrically shaped vesselpreferably three times. A wire mesh means is preferably provided and issecured at one end to stud means on the vessel. The fiberglassinsulation means is wrapped under the wire mesh means and the wire meshmeans is held somewhat taut so as to compress the fiberglass insulationmeans. With the mesh somewhat taut and the fiberglass insulation meanscompressed the insulation and mesh can be wrapped a plurality of timesabout the vessels and an elongated rod may be used intertwined in themesh to hold the mesh taut and in turn the insulation compressed. Asection of the outer jacket is then passed over the vessel and wrappedinsulation system. The rod may then be withdrawn to permit expansion ofthe insulation to substantially fill the void space defined between thevessel and the larger diameter outer jacket. After one end of the vesselhas been wrapped and an end of the outer jacket has been secured inplace then the insulation system of this invention is installed in asimilar manner at an inner section of the vessel and thereafter at theother end section of the vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

Numerous other objects, features and advantages of the invention willnow become apparent upon a reading of the following detailed descriptiontaken in conjunction with the accompanying drawings in which:

FIG. 1 shows a section of the inner vessel at an initial step ofapplying the insulation system of this invention;

FIG. 2 is a somewhat schematic view depicting the wrapping about theinner vessel;

FIG. 3 shows the insulation completely wrapped around the inner vesselwith the outer jacket about to be fitted over the inner vessel; and

FIG. 4 is a fragmentary view showing the vessel, jacket insulationsystem and securing rod in cross-section.

DETAILED DESCRIPTION

The drawings depict only a segment of the overall storage container thatis used for storing cryogenic liquids. The inner vessel is usuallyfabricated in two or three sections that are welded together in apredetermined sequence as the insulation system is applied and as theouter jacket also is fitted over the inner vessel. The outer jacket alsois preferably constructed in three separate sections including twolonger end sections and a relatively short middle section. The innervessel and the outer jacket are supported relative to each other by atleast one support cone welded in place therebetween. In the usualsequence of operation one end of the vessel is insulated, followed bythe insulation of the center section of the vessel in turn followed bythe insulation of the opposite end of the vessel. For some applicationsrequiring relatively small storage tanks the entire inner vessel may bewrapped in essentially a one-step operation.

Referring now to the drawings and in particular to FIGS. 1 and 2 thereis shown a section of inner vessel 10 which may be fabricated of SA-240type 304 stainless steel. The section of the vessel 10 shown in FIG. 1is welded to at least one other section to complete the entire closedvessel in which the cryogenic liquids are to be stored. A plurality ofstuds 12 are longitudinally arranged and are welded to the inner vessel10. As shown in FIG. 2 the wire mesh 14 is secured along one end to thestuds 12 and the studs 12 are provided with an enlarged head for holdingthe mesh securely. The wire mesh 14 is unwound from a roll 16 and as thewire mesh is rolled about the vessel section 10 a compressiblefiberglass insulation 18 is compressed between the wire mesh and thevessel. In the embodiment shown in FIG. 2 the wire mesh and theinsulation are wound about the vessel by rotating the vessel as shown bythe arrow in FIG. 2. The insulation is preferably constructed of smalldiameter fiberglass fibers (grade AA to grade B) either unbound or boundby heat or organic binders and is preferably provided in boards or battshaving a density of approximately 1 lb. per cu. ft. to 3 lbs. per cu.ft. As the mesh and insulation are wrapped about the vessel theinsulation is compressed by maintaining the mesh taut. This squeezingaction has the effect of increasing the density of the insulation to apreferred density range of from 4-6 lbs. per cu. ft.

FIGS. 3 and 4 show a later stage in the method of applying theinsulation to the cryogenic vessel. In the preferred embodiment the meshand insulation is wrapped about the vessel three times. To secure themesh in its taut condition and also to maintain the insulationcompressed so that the outer jacket 20 can be slid over the innervessel, there is provided an elongated rod or bar 22 which threadsbetween the top wrap and the next lower wrap to maintain the wire meshtaut. The jacket or jacket section 20 is then slid over the compressedinsulation and wire mesh. The bar 22 may then be withdrawn to allow theinsulation to expand to the interior walls of the jacket. The spacebetween the jacket 20 and vessel 10 is then evacuated to a pressure of,for example, 100 microns of mercury. At this pressure and at a densityof 4 lbs. per cu. ft. and with a mean temperature of -120° F. theinsulation of this invention has a thermal conductivity of about 0.05BTU-in/hr/sq.ft./° F. At atmospheric pressures under the sameconditions, the insulation of this invention has a thermal conductivityof 0.16 BTU-in/hr/sq.ft./° F.

Each section of the vessel can be wrapped in a similar manner asdiscussed with reference to FIGS. 1-4. Also, a conventional supportsystem may be used for supporting the vessel 10 relative to the jacket20. For example, a conical support may be welded to the open end of oneend section of the vessel. This conical support is also welded to oneend section of the outer jacket. The conical support is preferablyprovided at a central area of the overall length of the container.

What is claimed is:
 1. A method of insulating a cryogenic storage tankhaving a container vessel and an outer jacket with a space to beevacuated therebetween, comprising the steps of:providing a fiberglassinsulation means, wrapping the insulation means about at least a sectionof the vessel, providing a pervious means, securing an end of thepervious means to the vessel, wrapping the pervious means about thevessel with the insulation means being concurrently wrapped therewith,securing the pervious means at another end so that the insulation meansis compressed, and fitting the jacket at least partially over thevessel.
 2. A method as set forth in claim 1 wherein said previous meansincludes a mesh means that is wrapped about the vessel and comprisingthe further step of unsecuring the mesh means after the jacket is fittedto permit expansion of the fiberglass insulation means.
 3. A method asset forth in claim 2 wherein the mesh means is wrapped over thefiberglass insulation means.
 4. A method as set forth in claim 2 whereinthe mesh means is secured by an elongated rod which is later withdrawnto permit expansion of the fiberglass insulation means.
 5. A method asset forth in claim 2 wherein the insulation means is compressed from anormal density in the range of 1-3 pounds per cubic foot to a density inthe range of 4-6 pounds per cubic foot.